A variety of endeavors have been heretofore made for an internal combustion engine having a supercharger attached thereto for the purpose of preventing the temperature of a bearing portion for the supercharger from being elevated as a rotational shaft of the engine is rotated at a high speed and moreover improving the performance of the lubricant for cooling the bearing portion by bringing coolant into the bearing portion to cool it after the coolant flows through a housing of the engine to cool it.
FIG. 3 is an explanatory view which schematically illustrates the structure of a conventional apparatus for cooling an internal combustion engine having a water-cooled supercharger of the aforementioned type attached thereto.
With the conventional apparatus shown in FIG. 3, a housing of the engine is cooled in such a manner as described hereinafter.
In detail, coolant is cooled by radiating heat via a radiator b and the cooled coolant is then introduced into a coolant pump f via a lower tank of the radiator b, an outlet pipe d and a coolant inlet pipe e. The coolant pump f is driven by the engine so as to pump coolant through a coolant circulating passage g in the engine a to cool a cylinder block h, a cylinder head i and other components. It should be noted that FIG. 3 shows only a part of the coolant circulating passage g corresponding to the cylinder head i.
After coolant cools the interior of the engine a, it is finally brought into a thermostat housing j. The thermostat housing j includes a thermostat k for the purpose of regulating the flow rate of coolant adapted to flow through the radiator b by opening or closing a valve in the thermostat k depending on the coolant temperature.
Now, it is assumed that the temperature of coolant in the engine a is maintained at a level higher than an adequate temperature acceptable for operation of the engine a. In this case, the thermostat k is brought in an opened state so that coolant is delivered to an upper tank p on the radiator b via the thermostat k, a coolant outlet pipe l, a pipe m and an inlet pipe n.
Then, coolant is cooled down to an adequate temperature in the radiator b, and the thus cooled coolant is delivered to the engine a to cool it by circulating therethrough.
On the other hand, in a case where the temperature of coolant in the engine a is maintained at a level lower than the aforementioned adequate temperature, the thermostat k is closed so that coolant is delivered directly to the coolant inlet pipe e via a bypass pipe g without flowing through the radiator b to cool the coolant. In such manner, the temperature of coolant in the engine a is maintained at an adequate level.
The manner of cooling the housing of the engine a is as described above. Next, description will be made below as to cooling of the supercharger r.
Specifically, to cool the supercharger r the apparatus includes a coolant feed pipe t by way of which a part of the coolant circulating passage g corresponding to the cylinder block h communicates with a bearing portion s for the supercharger r as well as a return pipe u by way of which the bearing portion s communicates with the outlet pipe
With this construction, coolant in the coolant circulating passage g is delivered to a coolant flow passage in a center housing of the supercharger r via the coolant feed pipe t. As coolant flows through the coolant flow passage, heat exchange is accomplished between the coolant and the bearing portion s.
After completion of the cooling operation for the supercharger r, coolant flows through the return pipe u so that the flow of coolant is united with the flow of coolant which has cooled the interior of the engine a, in the outlet pipe l. Then, the flow of the combined coolant is delivered to the upper tank p. Thereafter, coolant is cooled in the radiator b by radiating heat therefrom.
As is well known, the bearing portion s of the supercharger r is heated up to an elevated temperature as a rotational shaft of the supercharger r is rotated at a high speed. Thus, coolant tends to be vaporized in the supercharger.
Further, as the coolant pump f is driven at a high coolant temperature, the negative pressure appearing at the suction portion of the coolant pump f comes near to a specific saturated steam pressure, whereby steam tends to be generated. Additionally, air and vapor tends to be involved entrained in coolant for the reasons as described above. Moreover, air in the outside environment may be introduced into the coolant circulating passage g via gaskets for the coolant circulating passage g.
Once air and vapor are entrained in the coolant, it may lead to malfunctions such as accelerated generation of cavitation, reduction of cooling efficiency, irregular local cooling due to the residual air or the like malfunction.
For the reason, there arises the necessity to effectively separate air and vapor from coolant.
To meet the necessity, arrangement is made such that an air vent pipe v extends between the upper end of the coolant circulating passage and the upper tank p and a coolant feed pipe w extends between the upper tank p and the coolant inlet pipe e.
With this arrangement, air in the coolant circulating passage g is delivered to the upper tank p together with a small quantity of coolant via the air vent pipe v. Air is separated from coolant in the upper tank p so that coolant with no entrained air is delivered to the coolant inlet pipe e via the coolant feed pipe so as to allow coolant to circulate through the interior of the engine a.
However, it has been found that the conventional apparatus as constructed in the above-described manner has the following problems.
In detail, on completion of a cooling operation for the supercharger r, coolant is delivered directly to the outlet pipe l without flowing into the thermostat housing j and then it is cooled in the radiator b by radiating heat therefrom. In other words, coolant which has cooled the supercharger r is cooled by radiating heat from the radiator b, even when the coolant has a temperature lower than the adequate temperature.
Thus, particularly in the winter season, coolant is brought in a so-called overcooled state having a temperature much lower than the adequate temperature. This leads to a result that the engine a can not be operated properly.
As is apparent from the drawing, the position where the outlet pipe l extends is set lower than the position assumed by the supercharger r. With this arrangement, air tends to return to the supercharger r side. Additionally, steam generated at the bearing portion s and other components remains, the joint portion between the return pipe u and the outlet pipe l. As a result, separation of air from coolant can not be accomplished completely.
The aforementioned type of apparatus should be constructed and fabricated with a reduced number of components and manhours at an inexpensive cost on a mass-production line.
The present invention has been made with the foregoing background in mind and its object resides in providing an apparatus for cooling an internal combustion engine having a supercharger attached thereto, wherein an occurrence of overcooling can reliably be prevented, air can completely be separated from coolant and the apparatus can advantageously be fabricated at an inexpensive cost on a mass-production line.